Method for producing an open-pore molded body which is made of a metal, and a molded body produced using said method

ABSTRACT

A method for producing open-pored molded bodies made of a metal. The surface of the metal open-pored molded body being used as a semi-finished product, is coated with particles of the same metal with which the semi-finished product is made or with particles of a chemical compound of the metal the semi-finished product is made, wherein the compound or particles can be reduced or thermally or chemically decomposed in a thermal treatment. After the coating process, a thermal treatment in a suitable atmosphere is carried out, in which the particles are connected to the surface of the semi-finished product and/or adjacent particles such that the specific surface area of the obtained open-pore molded body is increased to at least 30 m2/l and/or at least by a factor of 5 in comparison to the starting material.

BACKGROUND OF THE INVENTION

The invention relates to a process for producing an open-pored moldedbody or an shaped body comprising a metal and a molded body produced bythe process.

Coating porous metallic molded bodies on their surface in order, inparticular, to improve the properties is known. For this purpose, use iscustomarily made of pulverulent materials which are applied by means ofa binder or a suspension to surfaces of the molded body and organicconstituents are removed in a heat treatment and a coating or a surfaceregion which has a different chemical composition than the material ofwhich the shaped body was made can then be formed on surfaces of theshaped body at elevated temperatures.

The specific surface area of a shaped body can also be increased bymeans of these known possibilities, but this was possible to only alimited extent by means of the known possibilities.

However, very large specific surface areas are advantageous for manyindustrial applications, and is very desirable in, for example,catalytically assisted processes, filtration or in electrodes inelectrochemical applications.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide open-pored moldedbodies which are composed of a metallic material and have an increasedspecific surface area.

This object is achieved according to the invention by a process havingthe features of the independent claim which relates to a molded bodyproduced by the process. Advantageous embodiments and furtherdevelopments can be realized by means of the features in the dependentclaims.

In the invention, open-pored bodies composed of a metallic material areused as a semifinished part. These can be a metal grid, a metal mesh, awoven metal fabric, a metal foam, a metal wool or a semifinished partcomprising metallic fibers.

However, the semifinished part can also be an open-pored shaped body inwhich a polymer material has been electrochemically coated with a metal.A semifinished part produced in this way can be subjected to a thermaltreatment in which the organic and volatile constituents of this polymerare removed as a result of pyrolysis. However, this removal of theorganic constituents of a polymer can also occur later in a simultaneousremoval of other organic or volatile components, which will be discussedin more detail below. In one embodiment of the invention, this thermaltreatment is preceded or followed by

coating of the open-pored body with metallic particles composed of thesame metal material of which the open-pored semifinished part is made.Here, the particles should also be introduced into the interior of theshaped body, i.e. into the pores or voids of the semifinished part.

In a further embodiment of the invention, particles of a chemicalcompound of the chemical element present in the open-pored shaped bodyas semifinished part are applied by coating before or after this thermaltreatment. Said particles consist of a chemical compound which can beconverted in a thermal treatment by chemical reduction or thermal orchemical decomposition into the respective chemical element of which thesemifinished part is made.

The metallic particles of the same metal material from which theopen-pored semifinished part has been produced or the particles of achemical compound of the chemical element which can be converted intothe chemical element of which the open-pored molded body as semifinishedpart has been made can be used as powder, as powder mixture, assuspension or as dispersion for the coating operation. Coating of thesurface of the semifinished part with a powder, a powder mixture and/ora suspension/dispersion can be carried out by dipping, spraying, in apressure-assisted manner, electrostatically and/or magnetically.

In further alternatives according to the invention, the powders, powdermixtures, suspensions or dispersions used for coating the open-poredsemifinished part can contain not only metallic particles or particlesof a chemical compound of a metal but also an inorganic and/or organicbinder which is mixed in finely divided form as a solid powder into thepowder, the powder mixture, the suspension or dispersion or is presentdissolved in a liquid phase of a solution, a suspension/dispersion ofmetallic particles or particles of a chemical compound of a metal.

Coating of the surface of the semifinished part with a binder in theform of a solution or a suspension/dispersion can be effected by dippingor spraying.

The open-pored semifinished part which has been wetted with binder issubsequently coated with a powder or a powder mixture of metallicparticles.

The distribution of powder particles on surfaces which have been wettedwith the liquid binder and also the adhesion of the particles to thesurface can be improved by action of mechanical energy, in particularvibration.

The application of particles as powder, powder mixture and/orsuspension/dispersion can be repeated a number of times, preferably atleast three times, particularly preferably at least five times. Thisalso applies to the vibration to be carried out in each case andoptionally the application of a binder.

Coating of the surface of the semifinished part can also be carried outbefore the thermal treatment in which the organic constituents of thepolymeric material with the aid of which the semifinished part has beenproduced are removed. After application of the particle-containingmaterial, a thermal treatment in which organic and volatile constituentsof the polymeric material and at the same time any binder used areremoved is carried out.

After thermal treatment and application of particles, sintering in whichsinter necks or sinter bridges between the metal particles or frommetallic particles obtained by thermal or chemical decomposition, e.g. achemical reduction, to the metallic surface of the open-pored metallicmolded body are formed is carried out.

Here, the specific surface area of the open-pored molded body which hasbeen coated and sintered in this way should be increased to at least 30m²/l but at least by a factor of 5 compared to the starting material ofthe uncoated metallic shaped body as semifinished part.

Here, the porous basic framework having a pore size in the range from450 μm to 6000 μm and a specific surface area of 1 m²/l 30 m²/l shouldbe filled with particles (particle size d₅₀ in the range from 0.1 μm to250 μm), de-pending on the application either from one side (porositygradient) or completely or the struts of the porous metallic shaped bodyshould have been coated on the surface.

Coating with particles can be carried out using different amounts ondifferent sides of the surface, in particular on surfaces of thesemifinished part which are arranged opposite one another, in order toobtain a different porosity, pore size and/or specific surface area ineach case. This can, for example, be achieved by a different number ofapplications of particles as powder, powder mixture or insuspension/dispersion, with or without use of binder, on the surfacesarranged on different sides. A gradated formation of a molded bodyproduced according to the invention can also be achieved in this way.

The pore size within the applied particle layer of the coated andsintered open-pored molded body should correspond to not more than 10000 times the particle size used. This can be additionally influenced bythe maximum sintering temperature and the hold time at this temperaturesince mass transfer by diffusion and thus sintering, which is associatedwith a decrease in the pore volume, is promoted with increasingtemperature and hold time.

The material of which the molded body produced according to theinvention is made should contain not more than 3% by mass, preferablynot more than 1% by mass, of O₂. Preference is for this purpose given toan inert or reducing atmosphere while carrying out the thermal treatmentfor removing organic components, the chemical reduction which isoptionally to be carried out and/or the sintering.

For a thermal or chemical decomposition, a suitable atmosphere should beselected in the thermal treatment utilized for this purpose. This can inthe case of a thermal decomposition be an inert atmosphere, for examplean argon atmosphere. In the case of a reduction, it is possible toemploy, for example, an atmosphere of hydrogen.

For a chemical decomposition by means of oxidation, atmospherescontaining oxygen, fluorine, chlorine, any mixtures of these gases andalso any mixtures with inert gases, for example nitrogen, argon orkrypton, are particularly useful.

In the case of a chemical decomposition, metal cations can be reduced toform elemental metals. It is, however, possible to oxidize the anionconstituent. A chemical decomposition of a compound of relatively noblemetals to give the elemental metals (Au, Pt, Pd) in air, i.e. acomparatively oxidizing atmosphere, is also conceivable.Disproportionations according to the illustrative equation: 2 Gel<->Ge(s)+Gel (g) are also possible for aluminum, titanium, zirconium andchromium. It is also possible to use crystalline, metal-organiccomplexes or salts thereof in which the metal center is already in theoxidation state 0.

It is also possible to employ such an open-pored molded body producedaccording to the invention in the field of (i) filtration, as (ii)catalyst (e.g. in the synthesis of ethylene oxide using an Ag foamcatalyst coated with Ag particles), as (iii) electrode material or as(iv) support for a catalytically active sub-stance.

Increasing the specific surface area leads, in the case of application(i), to a better filtration performance since adsorption tendency anduptake capacity are significantly increased.

In application (ii), the increase in the specific surface area leads toa greater than proportional increase in the catalytic activity since notonly does the number of active centers increase but the surface also hasa distinctly faceted structure. The resulting increased surface energyadditionally leads to a significant increase in the catalytic activitycompared to the unfaceted surface of the open-pored starting shapedbody.

In application case (iii), the increase in the specific surface arealikewise leads to an increase in active centers, which in combinationwith the faceted structure of the surface leads to a significantreduction in the electric overvoltage compared to commercial electrodes(e.g. nickel or carbon). As specific application, mention may also bemade of electrolysis, e.g. using Ni or Mo foam coated with Ni particlesor Mo particles. In this application in particular, it is alsoadvantageously possible to use sintered metallic open-pored moldedbodies coated on one side with metallic particles since in this case thegradation of the pore size ensures that the gas bubbles are transportedaway well.

In the case of application (iv), the increase in the specific surfacearea leads to better adhesion of the active component, e.g. a catalyticwashcoat, to the support surface, which significantly increases themechanical, thermal and chemical stability of a catalyst material.

Suitable metals for molded bodies produced according to the inventionare: Ni, Fe, Cr, Al, Nb, Ta, Ti, Mo, Co, B, Zr, Mn, Si, La, W, Cu, Ag,Au, Pd, Pt, Zn, Sn, Bi, Ce or Mg. Particles of these elements,corresponding to the respective chemical element of which thesemifinished part is made, can accordingly be used in the process of theinvention for coating a semifinished part.

As chemical compounds of the metals Ni, Fe, Cr, Al, Nb, Ta, Ti, Mo, Co,B, Zr, Mn, Si, La, W, Cu, Ag, Au, Pd, Pt, Zn, Sn, Bi, Ce, Mg, V whichcan be converted by thermal or chemical decomposition in a thermaltreatment into particles of the respective metal it is possible to use,in particular, their oxides, nitrides, hydrides, carbides, sulfides,sulfates, phosphates, fluorides, chlorides, bromides, iodides, azides,nitrates, amines, amides, metal-organic complexes, salts ofmetal-organic complexes or decomposable salts for the material formedwith particles, with which the surface of the open-pored shaped bodypresent as semifinished part is to be coated in the second alternativeaccording to the invention. Particularly suitable chemical compounds arechemical compounds of: Ni, Fe, Ti, Mo, Co, Mn, W, Cu, Ag, Au, Pd or Pt.

In the thermal or chemical decomposition of a chemical compound to givethe respective metal, an atmosphere suitable for the decomposition,which can be inert, oxidizing or reducing, is maintained until thethermal or chemical decomposition of the chemical compound into themetal has occurred. For the chemical reduction of a chemical compound tothe respective metal, the thermal treatment which is to lead to thechemical reduction can preferably be carried out in a reducingatmosphere, in particular a hydrogen atmosphere, for at least some ofthe time until the chemical reduction has been carried out.

Porosity, pore size and specific surface area can be substantiallyinfluenced by the morphology of the particles used for the coating. Toachieve a high specific surface area and a finely porous structure,particles having a small size and a dendritic shape, e.g. electrolytepowders, are advantageous. As a result of their irregular geometry whichdoes not allow a gap-free arrangement, adjacent particles form voidswhich are partially connected to give channels between contact pointsand particle bodies. Furthermore, an additional micropore space leftbehind by the volatile component is formed in the thermal decompositionor chemical decomposition when using particles of a chemical compound.The greater the proportion of the volatile component of the chemicalcompound, the higher the proportion of the micropore space in the totalpore volume. The use of an oxide having a high oxidation state andconsequently a high proportion of oxygen is therefore advantageous for acoating with metal oxide particles. Since the sintering activity ofstructures increases with increasing specific surface area, thematerial-dependent sintering temperature is chosen so as to be just highenough for the particles to sinter to one another and to thesemifinished part in a mechanically stable manner without the fine poresbeing significantly densified.

DETAILED DESCRIPTION OF THE INVENTION

The invention will be illustrated below with the aid of examples.

Working Example 1

As semifinished part, an open-pored shaped body composed of silver,average pore size 450 μm, having a porosity of about 95% and thedimensions 70 mm×63 mm, thickness 1.6 mm (produced by electrolyticdeposition of Ag on polyurethane foam), is subjected to a thermaltreatment at a temperature of at least 400° C. in order to remove theorganic components, especially those of the polyurethane.

To increase the specific surface area, a metallic powder, namely Agmetal powder having a particle size d₅₀ in the range from 3 μm to 9 μm,is used in a total amount of 2 g.

Coating of the surface of the metallic open-pored shaped body assemifinished part is carried out using 0.6 g of stearamide wax having aparticle size of <80 μm and a 1% strength aqueous solution ofpolyvinylpyrrolidone having a volume of 6 ml as binder. The surface ofthe semifinished part is sprayed with the binder solution, including inthe interior of pores, before the silver powder is applied to thesurface coated with the binder.

Silver powder and the stearamide wax were mixed for 10 minutes using aTurbula mixer.

After this coating with binder, the open-pored coated shaped body wasfixed in a vibration apparatus and sprinkled on both sides with thesilver powder. The powder is distributed uniformly in the open-porenetwork by means of the vibration. The particles adhere only to thestrut surface, so that the struts are completely covered with powderparticles and the open porosity of the foam is retained. The procedureis repeated four times.

Subsequently, a further thermal treatment is carried out in a hydrogenatmosphere to effect binder removal and sintering. For this purpose, thefurnace is heated up at a heating rate of 5 K/min. Binder removalcommences at about 300° C. and is concluded at 600° C. and a hold timeof about 30 minutes. The sintering process takes place in thetemperature range from 550° C. to 850° C. at a hold time of from 1minute to 60 minutes.

During the further thermal treatment, the Ag diffuses out of the powderparticles into the strut material until the powder particles, via sinternecks or sinter bridges thereby formed, are firmly joined to the strutsof the surface of the semifinished part.

After the further thermal treatment, the open-pored molded bodyconsisted of 100% of silver. The porosity was about 94%.

The surface of the struts has a high roughness. The reason for this isthat the applied powder particles are joined only via sinter necks orsinter bridges to the metallic support foam of the semifinished part, sothat the original particle morphology is retained. The specific internalsurface area (measured using the BET method) of the finished open-poredmolded body could be increased from 10.8 m²/l initially (uncoated state)to 99.3 m²/l afterwards (coated state).

Working Example 2

An open-pored shaped body composed of silver as semifinished part havingan average pore size of 450 μm, a porosity of 95%, the dimensions 70mm×63 mm, thickness 1.6 mm, obtained by electrochemical coating of aporous foam composed of polyurethane, was subjected to a thermaltreatment to remove the organic components, as in working example 1.

Surfaces of the semifinished part which had been freed of organiccomponents were subsequently coated by spraying with a suspension havingthe following composition:

-   -   48% Ag₂O metal oxide powder<5 μm,    -   1.5% polyvinylpyrrolidone (PVP) binder    -   49.5% water as solvent    -   1% dispersant.

For this purpose, the pulverulent binder was firstly dissolved in waterand then all other components were added and mixed in a Speedmixer for2×30 seconds at 2000 rpm to give a suspension.

The semifinished part was sprayed with the prepared powder suspension anumber of times on both sides by a wet powder spraying process. Here,the suspension is atomized in a spraying device and applied to surfaceson both sides of the semifinished part. The suspension is distributeduniformly in the porous network of the semifinished part by the exitpressure from the spray nozzle. The suspension adheres only to the strutsurface, so that the struts are completely covered with the suspensionand the open porosity of the semifinished part is largely retained. Thesemifinished part which has been coated in this way was subsequentlydried in air at room temperature.

For binder removal, reduction and sintering, a thermal treatment wascarried out under a hydrogen atmosphere and subsequently in a furnace.For this purpose, the furnace was heated up at a heating rate of 5K/min. The reduction of the silver oxide commences at below 100° C. andis concluded at 200° C. and a hold time of about 30 minutes underhydrogen. The remaining binder removal and sintering process can then becarried out in an oxygen-containing atmosphere, e.g. air, in thetemperature range from 200° C. to 800° C. at a hold time of from 1minute to 180 minutes.

During the further thermal treatment, the silver oxide was firstlyreduced to metallic silver, which is present in nanocrystalline form. Asa result of the remaining binder removal and partial sintering of thethen metallic silver particles onto the silver foam struts, theparticles grow to form larger and more coarsely crystallineconglomerates, and secondly the Ag also diffuses out from the powderparticles into the strut material until the powder particles are firmlyjoined via sinter necks or sinter bridges which form to the struts ofthe surface of the open-pored molded body.

After the further thermal treatment, a homogeneous open-pored moldedbody which is formed by 100% silver is present.

The porosity is about 93%.

The surface of the struts has a high roughness. The reason for this isthat the applied powder particles are joined only via sinternecks/sinter bridges to the surfaces of the semifinished part, so thatthe original particle morphology is retained. The specific internalsurface area (measured by the BET method) of the finished open-poredmolded body was able to be increased from 10.8 m²/l initially (uncoatedstate) to 82.5 m²/l afterwards (coated state) by means of the processcarried out.

Working Example 3

An open-pored shaped body composed of copper and having an average poresize of 800 μm, a porosity of about 95%, the dimensions 200 mm×80 mm,thickness 1.6 mm (produced by electrolytic deposition of Cu on PU foam),was used as semifinished part.

Electrolytic copper powder of the type FFL, having a dendritic form, anaverage particle size of <63 μm and a mass of 20 g, was used as powderfor coating surfaces of the semifinished part.

A 1% strength aqueous solution of polyvinylpyrrolidone having a volumeof 20 ml was used as binder.

The semifinished part composed of copper was sprayed with the bindersolution on both sides. The binder-coated semifinished part wassubsequently fixed in a vibration apparatus and sprinkled on both sideswith the copper powder. The powder is distributed in the porous networkof the semifinished part by the vibration. The binder and powder coatingwas repeated three times, so that the pore space had been filledcompletely.

Binder removal and sintering were carried out in a thermal treatmentunder a hydrogen atmosphere. For this purpose, the furnace was heated upat a heating rate of 5 K/min. Binder removal commences at about 300° C.and is concluded at 600° C. and a hold time of about 30 minutes. Heatingup is then continued up to a sintering temperature of 950° C. and thistemperature was maintained for 30 minutes.

During the thermal treatment, the powder particles composed of coppersinter to one another and to the strut material until the powderparticles are firmly joined via sinter necks or sinter bridges whichform to the surface of the semifinished part, with a high porosity beingretained and an increase in the specific surface area being achieved.The porosity of the open-pored molded body treated in this way is 54%and the specific surface area is 67 m²/I.

Working Example 4

An open-pored shaped body made of cobalt and having an average pore sizeof 580 μm, a porosity of about 95%, the dimensions of 70 mm×65 mm,thickness 1.9 mm (produced by electrolytic deposition of Co on PU foam),was used as semifinished part, Co metal powder having an averageparticle size of <45 μm and a mass of 10 g and also stearamide waxhaving a particle size of <80 μm and a mass of 0.1 g was used as powder,and a 1% strength aqueous solution of polyvinylpyrrolidone having avolume of 6 ml was used as binder.

Cobalt powder and stearamide wax were mixed for 10 minutes using aTurbula mixer.

The semifinished part composed of cobalt was sprayed on one side withthe binder solution. It was subsequently fixed in a vibration apparatusand sprinkled on both sides with the cobalt powder. As a result of thevibration, the powder is uniformly distributed in the porous network ofthe semifinished part. The particles adhere only to the strut surface,so that the struts are completely covered with powder particles and theopen porosity of the foam is initially retained. In a second step, thesurface of the semifinished part is sprayed with binder solution on afirst side to such a degree that the previously open pores are closed onone side by the binder, and the pore space close to the surface iscompletely filled by the subsequent further application of powder. Onthe opposite side of the semifinished part, only the struts are coatedon the surface. As a result, the powder loading and thus the porosity inthe foam is gradated from the first side to the opposite side of thesemifinished part.

For binder removal and sintering, a thermal treatment was carried out ina hydrogen atmosphere. For this purpose, the furnace was heated up at aheating rate of 5 K/min. Binder removal commences at about 300° C. andis concluded at 600° C. and a hold time of about 30 minutes. This isfollowed by heating up to a sintering temperature of 1300° C. and thistemperature maintained for 30 minutes.

During the thermal treatment, the Co diffuses out of the powderparticles into the strut material of the semifinished part until thepowder particles are firmly joined via sinter necks or sinter bridgeswhich form both to the struts and also (in the completely filledregions) to one another.

The Co content of the finished open-pored molded body was 100%. Theporosity is gradated over the total thickness of the molded body fromthe first side to the side located opposite the first and is about 54%on one side and about 93% on the other foam side. The specific surfacearea of the finished open-pored molded body is 69 m²/I.

Working Example 5 (Ni Expanded Metal Mesh+Ni Powder→UniformCoating+Sintering

1. Material

An open-pored nickel expanded metal mesh having a cell size of about 0.7mm×2 mm and the dimensions 75 mm×75 mm, thickness about 1 mm (producedby stretching an originally 0.25 mm thick slotted Ni sheet) was used assemifinished part, Ni metal powder having an average particle size of<10 μm and a mass of 8 g, a stearamide wax having an average particlesize of <80 μm and a mass of 0.2 g, was used as metal powder and a 1%strength aqueous solution of polyvinylpyrrolidone having a volume of 4ml was used as binder.

Powder and stearamide wax were mixed for 10 minutes using a Turbulamixer.

The nickel expanded metal mesh was sprayed with the binder solution fromtwo opposite sides. The mesh was subsequently fixed in a vibrationapparatus and sprinkled on both sides with the nickel powder. As aresult of the vibration, the nickel powder is uniformly distributed onthe mesh. The particles adhere only to the mesh strut surface, so thatthe mesh struts are completely covered with powder particles and theopen porosity of the expanded metal mesh is retained. The procedure wasrepeated five times.

Binder removal and sintering were carried out in a thermal treatmentunder a hydrogen atmosphere. For this purpose, the furnace was heated upat a heating rate of 5 K/min. Binder removal commences at about 300° C.and is concluded at 600° C. and a hold time of about 30 minutes. Heatingup was then continued up to a sintering temperature of 1280° C. and thistemperature was maintained for 30 minutes.

During the thermal treatment, the Ni diffuses out of the powderparticles into the mesh strut material until the powder particles arefirmly joined via sinter necks or sinter bridges which form to the meshstruts.

The open-pored molded body obtained in this way consisted of 100% ofnickel.

The surface of the struts has a high roughness since the applied powderparticles are joined only via sinter necks or sinter bridges to thesupport mesh of the semifinished part and to one another, so that theoriginal particle morphology is largely retained. The appliedhigh-porosity nickel layer on the struts has a thickness of from 1 μm to300 μm. The porosity within the applied layer is 40%.

1. A process for producing open-pored molded bodies comprising a metal,wherein an open-pored shaped body comprising metal as a semifinishedpart is coated on its surfaces with particles of the same metal, ofwhich the semifinished part is formed or is coated with particles of achemical compound of the metal of which the semifinished part is made,which chemical compound can be reduced or thermally or chemicallydecomposed in a thermal treatment and being formed by particles of therespective metal obtained by chemical reduction or thermal or chemicaldecomposition; and the coating is followed by at least one thermaltreatment in which the particles are joined via sinter necks or sinterbridges to the surface of the semifinished part and/or adjacentparticles so that the specific surface area of the open-pored moldedbody obtained is increased to at least 30 m²/l and/or by at least afactor of 5 compared to the starting material of the uncoated metallicsemifinished part, with a metal reducing atmosphere or an atmospheresuitable for the decomposition is maintained in the thermal treatment ofa coated open-pored shaped body with particles of a reducible orthermally or chemically decomposable chemical compound of the metal ofwhich the semifinished part is made, at least until the reduction orthermal or chemical decomposition of the chemical compound to form themetal is complete.
 2. The process as claimed in claim 1, wherein theparticles of a metal or the particles of a chemical compound of themetal are used as powder, powder mixture and/or suspension/dispersion.3. The process as claimed in claim 1, wherein the application of theparticles of the metal or the particles of the chemical compound of themetal as powder, powder mixture, suspension and/or dispersion is carriedout by dipping, spraying, in a pressure-assisted manner,electrostatically and/or magnetically.
 4. The process as claimed inclaim 1, wherein an organic and/or inorganic binder is used in solution,suspension/dispersion or as a powder in order to improve the adhesion ofparticles.
 5. The process as claimed in claim 1, wherein the applicationof particles of the metal or particles of the specified chemicalcompound of the metal is repeated a number of times.
 6. The process asclaimed in claim 1, wherein in the case of multiple coating withparticles of the metal or particles of the chemical compound of themetal, when a binder is employed, the application of the binder isrepeated a number of times.
 7. The process as claimed in claim 1,wherein the application of a binder and the application of the particlesof the metal or the particles of the chemical compound of the metal iscarried out on different sides of the surface of the semifinished partusing different amounts in order to obtain a different porosity, poresize and/or specific surface area.
 8. The process as claimed in claim 1,wherein Ni, Fe, Cr, Al, Nb, Ta, Ti, Mo, Co, B, Zr, Mn, Si, La, W, Cu,Ag, Au, Pd, Pt, Zn, Sn, Bi, Ce or Mg is used as metal for thesemifinished part and the particles to be applied or a chemical compoundof Ni, Fe, Cr, Al, Nb, Ta, Ti, Mo, Co, B, Zr, Mn, Si, La, W, Cu, Ag, Au,Pd, Pt, Zn, Sn, Bi, Ce or Mg, is used as metal for the semifinished partand particles of a reducible, thermally or chemically decomposablecompound of this metal.
 9. The process as claimed in claim 1, wherein asemifinished part which has been obtained by electrochemical coating ofan open-pored body of a polymeric material with the respective metal isused as semifinished part.
 10. A coated and sintered open-pored moldedbody produced by a process wherein the molded body with metallicparticles joined via sinter necks or sinter bridges to the surface of asemifinished part and/or the surface of adjacent particles has aspecific surface area of at least 30 m²/1.
 11. The coated and sinteredopen-pored molded body as claimed in claim 10, wherein pore size withinthe coated and sintered open-pored molded body corresponds to not morethan 10 000 times the particle size used.
 12. The coated and sinteredopen-pored molded body as claimed in claim 10, wherein not more than 3%by mass of oxygen is present in the material of the coated and sinteredopen-pored molded body.